Unfortunately, claimed waranties for items sold on eBay are liable to be non-existent or worthless.
Buying from unknown sellers isn't like buying from the shops. eBay even warns buyers in the user agreement that they do not guarantee the quality of items sold here, that they will be truthfully described, safe or even legal. Would you have bought from a shop that stated this?? But these are the risks you accept on eBay.
As has been said, it's too late for any halp from eBay, but if the seller is a UK business seller you could talk with citizens advice about any consumer rights you may have. But be aware that having rights and being able to enforce them are not the same thing!